Mirena sharp pains

I got my mirena placed almost a year ago. My periods are very irregular now and they said that I will most likely not have one after 3 months. I also get very strong, sharp pains that feel like extreme cramps. It's almost like my uterus is squeezing the I'd causing the pain. It's hard to explain, but does anyone else experience this? I'm only 20 and I have never had any kids.